First, spread spectrum wireless communications will be described. In typical communications using the spread spectrum technology, a transmitting end performs spectrum spreading using a spread code on a modulation signal which is obtained by modulating an input baseband signal such as sound, and sends the resultant spread spectrum signal as a high frequency signal (RF signal) to a receiving end. The receiving end demodulates (despreads) the spread spectrum signal sent from the transmitting end using the same spread code as that used in the transmitting end.
Further, the communication method using the spread spectrum technology includes direct sequence spread spectrum (DSSS) and frequency hoping spread spectrum. The DSSS multiplies a narrow-band modulated signal by a spread code to spread the signal evenly over a certain continuous band of frequencies. On the other hand, the frequency hopping spread spectrum randomly changes a carrier frequency using a spread code to spread the signal over a band of frequencies. Bluetooth is an exemplary application of the frequency hopping spread spectrum.
The following will explain a conventional card type wireless communication apparatus. FIG. 12 is a block circuit diagram showing schematic configuration of the conventional card type wireless communication apparatus. The conventional card type wireless communication apparatus 100 shown in FIG. 12 is so configured that an antenna 101 is connected to a receiver circuit section 102, and to a transmitter circuit section 107.
The receiver circuit section 102 is composed of an amplifier 103, a mixer circuit 104, and a demodulator circuit 105. The antenna 101 is connected to a baseband signal processing circuit section 111 through the amplifier 103, the mixer circuit 104, and the demodulator circuit 105.
The transmitter circuit 107 is composed of a modulator circuit 110, a mixer circuit 109, and an amplifier 108. The baseband signal processing circuit section 111 is connected to the antenna 101 through the modulator circuit 110, the mixer circuit 109, and the amplifier 108. The mixer circuit 104 and the mixer circuit 109 are connected to a local oscillator 106.
Further, the baseband signal processing circuit section 111 is connected to a connector 115 through an interface circuit section 112. The receiver circuit section 102, the transmitter circuit section 107, and the baseband signal processing circuit section 111 are connected to a circuit control section 113. A power source section 114 is connected to the connector 115 and to each of the above-described circuits in the card type wireless communication apparatus 100.
Next, the operation of the conventional card type wireless communication apparatus 100 shown in FIG. 12 will be described. A spread spectrum signal (e.g. 2.4 GHz band) from the transmitting end is received by the antenna 101 of the receiving end. Then, the spread spectrum signal is amplified by the amplifier 103, and is applied to the mixer circuit 104. The received high frequency signal (the spread spectrum signal) is demodulated to a baseband signal by the mixer circuit 104 and demodulator circuit 105. The baseband signal is subjected to necessary signal processing conducted by the baseband signal processing circuit section 111, and is then outputted through the interface circuit section 112 to an information terminal device such as a personal computer (not shown).
At the transmitting end, a data input signal supplied from the information terminal device such as a personal computer (not shown) through the connector 115 and interface circuit section 112 is subjected to necessary signal processing conducted by the baseband signal processing circuit section 111, and is spread to a spread spectrum signal (e.g. 2.4 GHz band) by the modulator circuit 110 and mixer circuit 109. The data signal is then amplified by the amplifier 108, and is transmitted via the antenna 101 to the receiving end.
The circuit control section 113 controls the operation of the receiver circuit section 102, the transmitter circuit section 107, and the baseband signal processing circuit section 111. The power source section 114 receives power through the connector 115 from the information terminal device such as a personal computer (not shown), and supplies power +B to each circuit described above in the card type wireless communication apparatus 100.
The local oscillator 106 generates necessary frequency signals (e.g. 2.4 GHz band) for the operation of each of the mixer circuits 104 and 109.
For controlling RF signals of a wireless section, various types of communication apparatuses modulate and demodulate signals of different frequencies and levels by converting the frequencies of the signals, and therefore require stable modulation and demodulation characteristics.
Here, one of the most important factors is an input dynamic range. The input dynamic range indicates a range of input signals from the weakest to the strongest that can be stably received and demodulated.
For a wireless communication apparatus having receiver and transmitter circuits, the dynamic range is determined mainly by parameters such as transmission (high frequency) power, receiving sensitivity, and a distortion property.
For a short distance communication in which a distance between a host (master) (access point, a router, a transmission box, etc.) and a client (slave) is short, one of conventional arts for attaining a larger communication range is to prevent deterioration in distortion property with respect to a strong input signal by using an attenuator in an input stage of a receiver, or by lowering a gain of a low noise amplifier or an IF amplifier (see Japanese Publication of Utility Model, Jitsukaihei, No. 4-116440; published on Oct. 29, 1992).
FIG. 13 shows an example of the conventional art. In FIG. 13, an attenuator circuit (RF ATT) 140 is provided in between an input terminal 121 for a high frequency input signal and a high frequency amplifier 128. The attenuator circuit 140 is composed of a high frequency amplifier 141, an attenuator 142, a switch 143 that selectively connects the high frequency amplifier 141 or the attenuator 142 to the input terminal 121, and a switch 144 that selectively connects the high frequency amplifier 141 or the attenuator 142 to the high frequency amplifier 128.
Note that, in FIG. 13, there are provided a high frequency bandpass filter (RFBPF) 129, a mixer (MIXER) 130, a first voltage controlling oscillator (VCD1) 131, a first IF amplifier (IFAMP) 132, an IF bandpass filter 133, a second IF amplifier 134, an FM detector (FMDET) 135, a second voltage controlling oscillator 136, and an output terminal 137 for outputting a detected signal. These circuits are conventionally well known, thus their explanation is omitted here.
Incidentally, a mobile wireless communication apparatus is particularly required to reduce its power consumption in order to operate for a longer time. Here, a circuit similar to the attenuator circuit (RF ATT) 140 may be provided as a power amplifier for amplifying transmission power, so that the size of the transmission power is changed according to conditions. With this arrangement, by reducing the transmission power when the transmission power is not required much, it is possible to reduce the power consumption without narrowing the communication range.
However, in the arrangement in which the power source voltage of the power amplifier is fixed, it is difficult to sufficiently reduce the power consumed by the power amplifier. Accordingly, further reduction of the power consumption is demanded. Note that, the reduction of power consumption and occupying area is especially required for a mobile wireless communication apparatus, but also preferably required for a stationary apparatus.